Screw driven tailgate loader



Oct. 13, 1959 M. T. REED, JR

SCREW DRIVEN TAILGATE LOADER 3 Sheets-Sheet 1 Filed Feb. 12, 1958 .illlulllllllnll ll|l||||||||||| L II 1N VENTOR d AT4IO EY Get. 13, 1959 M. T. REED, JR

SCREW DRIVEN TAILGATE LOADER 3 Sheets-Sheet 2 Filed Feb. 12, 1958 E E C E E E I E E c E E E E z r I: c C C E z r r 5 f c 2 E E II E- INVENTOR -50 5 916W 6: @4424) 54/. dt 44 M ATTO EY Oct. 13, 1959 M. T. REED, JR 2,908,408

SCREW DRIVEN TAILGA'IE LOADER Filed Feb. 12, 1958 3 Sheets-Sheet 3 2,908,408 SCREW DRIVEN TAILGATE LOADER Maurice T. Reed, Jr., Jackson, Miss. Application February 12, 1958, Serial No. 714,893 14 Claims. (Cl. 214-75) My invention relates broadly to tailgate loader mechanisms and more particularly to a construction of truck tailgate loader using vertically mounted drivescrews to raise and lower a tailgate lift platform.

One of the objects of my invention is to provide a construction of screw driven tailgate loader which may be manufactured in mass production at relatively low cost and with less skilled workers than existing tailgate loaders and yet operate very reliably.

Another object of my invention is to provide a construction of screw driven tailgate loader in which no bending moment or torsional bending moment can be transferred to the vertically mounted drive screws by the movable portion of the tailgate or the load being moved.

Another object of my invention is to provide a construction of screw driven tailgate loader in which the load on the moveable portion of the tailgate loader is exerted through the center axis of the vertical drive screws by means of simple ball bearings mounted along a common center line through the diameters of the two drive screws.

Still another object of my invention is to provide a construction of screw driven tailgate loaders for which there is wide latitude in the lifting height to which the loader may economically perform. V

A further object of my invention is to provide a construction of screw driven tailgate loader in which sticking of lift channels which slide within lift track support channels of the loader are automatically freed during the downward travel of the lift channels.

Other and further objects of invention reside in the methods and construction used to transfer power from the vertical drive screws to the tailgate lift platform, and the spring loaded friction ball construction used to prevent jamming of the loader driving mechanism as set forth more fully in the specification hereinafter following by reference to the accompanying drawings, in which:

Fig. 1 is a side elevational view of the screw driven tailgate loader of my invention mounted on a truck and particularly showing the extreme upper and lower positions of the tailgate lift platform and the manner in which it is moved into the vertical plane to form the truck tailgate;

Fig. 2 is a rear elevational view partly in section of the screw driven tailgate loader of my invention particularly showing the dual screw driven lift mechanisms con trolled by a common drive shaft; v

Fig. 3. is a vertical sectional view taken substantially along line 3-.-3 of Fig. 2 showing the overall screw driven lifting mechanism; I V Fig; '4is an enlargedjview partly in section of .a fragmentary portion of Fig, 3 andparticular'ly showing. the principalfc'onrponents of the lift channel frictionjjball loading device;

Fig 5 is an elevational view of the top portion ofa I platform channel'as seen from'the solid" face side States Patent lifting mechanism and the i 2,tltl8,4tl8 Patented Oct. 13, 1959 and particularly showing a back view of the lift channel friction ball loading device and the mounting of the hardened steel plate and its association with the steel lift balls;

Fig. 6 is a cross sectional View taken substantially along line 66 of Fig. 4 and particularly showing the close spatial relation between the block on the drive screw and the associated channels and the placement of the steel lift balls along the drive screw center line;

Fig. 7 is a cross sectional view taken substantially along line 7-7 of Fig. 4 and particularly showing the clearance provided between the drive screw and the restraining and hardened steel bearing plates;

Fig. 8 is a cross sectional view taken substantially along line 8-8 'of Fig. 4 and particularly showing one of the mating helical gear driving mechanisms; and

Fig. 9 is a partial side elevational view of the tailgate loader of my invention showing a hand crank attached to the drive shaft as a modified form of driving means rather than the power driving means shown in Figs. 1 and 2.

My invention is directed to the construction of a screw driven truck tailgate loader wherein a drive screw driven by a common drive shaft is vertically mounted in a U- shaped support channel on either side of the truck tailgate. The drive shaft, rotated by either manual or power means, rotates each drive screw through a set of helical gears. An internally threaded block is carried by each drive screw which travels up and down the length of the screw when it is rotated; the direction of block travel depending upon the direction of drive screw rotation. A platform lift channel is arranged within each support channel so it can travel up and down in a vertical plane within said support channel. A tailgate lift platform pivotally attached between the two platform lift channels at their lower ends forms a load lifting platform when in the horizontal position and a truck tailgate when pivoted into the vertical plane after it has been raised to truck bed height.

The up and down movement of the platform lift channels is controlled by the blocks traveling up and down on the drive screws, the top of the lift channels being cou pled to the drive screw blocks by means of steel balls inserted on the top of the blocks bearing on hardened steel plates firmly attached to the tops of the lift channels. As the blocks travel upward on the drive screws the balls transfer an upward force to the lift channels thus carrying the lift channels upward. When the blocks travel downward on the drive screws the balls lower the lift channels which descend under their own weight. If on the downward movement the channels stick or hang-up within each other the drive screw blocks will continue downward until they encounter the spring loaded friction balls of the lift channel friction ball lowering device protruding throughthe back wall of the lift channels. When the blocks and friction balls thus encounter, the blocks impart a downward force on the friction balls which in turn transferv this force to the lift channels resulting in the blocks dragging the lift channels downward, thus freeing the sticking channels. This device only comes into play during downward travel of the tailgate lift platform. Use. of this device and the block and screw lift mechanism allows, the tailgate loaders to be manufactured much cheaper .since manufacturing tolerances do not have to be confined within narrow limits to produce a satisfactory trouble free tailgate loader.

Referring to the drawings in greater detail reference character 1 designates the. tailgate lift platform pivotally attached at. 2' on either'sid'e thereof to supporting brackets 4 which in turn are securely attached at the bottom of two identical platform lift channels of U-shapedcross section shown'at 3. Tailgate lift platform 1 and the two 3 V platform lift channels 3 move as one integral unit and substantially comprise that portion of the tailgate loader of my invention that travels up and down in the vertical plane carrying the load. Since an identical lift mechanism is disposed on either side of the tailgate, similar reference characters will designate correspondingly similar members on either side of said tailgatethroughout this specification. A

Platform lift channels 3 are enclosed within steel support channels 5, each of which consists of lift track members 5a and 5c welded to back member 5b to form a channel of U-shape cross-section. Soft metal restraining bars 6 and 7 disposed within the U of each support channel 5 restrain the lateral movement of each platform lift channel 3, whose smaller U-shaped cross-section is disposed opposite to that of the support channel, in two of the four lateral directions. Movement of the platform lift channels in the other two lateral directions is re- .1

strained by magnetized lateral anti-friction channel balls 8, disposed in depressions on the external lateral surfaces of the legs of the U-shaped platform lift channels 3 at symmetrical distances along the length of the platform lift channels, bearing and rolling on the internal surfaces of lift track members 501 and 5c of support channels 5. The lateral anti-friction channel balls 8 are discussed in greater detail in my co-pending application, Se-

rial No. 712,784, filed Feb. 3, 1958, for Chain Driven 4 22' and engage Same through slots 23 in support channel back members 5b and horizontal angle member 9. Drive shaft 27 extends across the width of the U-shaped structure and is located beneath bedplate 11 and encased between horizontal angle members 9 and 12 and is mounted in bearings 28 at either end thereof, which bearings are bolted to back member 5b of each support channel. With this construction drive shaft 27 is completely and easily removable from the tailgate supporting structure for servicing and/ or replacement.

The screw driven tailgate leader of my invention may be adapted with either manual driving means as seen in A Fig. 9 or with power driving means as seen in Figs. 1

and 2. In the manually driven model a hand crank lever 29 is attached directly to the end of drive shaft 27 and pressure on the hand crank lever will readily rotate drive screws through the helical gears and lift a load of the maximum specified. weight on tailgate lift platform 1. On the power driven model drive shaft 27 is rotated by motor 30 through gear box 31 and gear reducer 32. The gear ratios of gear box 31 and gear reducer 32 can be varied to give any desired commercial rate of lift. The above mentioned components which make up the power mechanism are attached directly to the side of Electric Tailgate Loader. Thus the platform lift channels are restricted to movement in the vertical plane within the support channels.

' The stationary portion of the screw driven tailgate loader of my invention, that is, the portion which bolts to the truck body is a U-shaped welded structure comprised of p a support channel 5 welded in the vertical position to either end of horizontal angle member 9 with gusset plates 10 welded between the adjacent members for ri idity, bed plate 11 reinforced with angle member 12,

welded to the top of horizontal angle member 9 to form a mounting sill, angle plate 13 welded to the back of right support channel 5 (as seen in Fig. 2) and top of bed plate 11 to form a truck mounting plate, and adjustment plate 14 of the truck width adjustment assembly welded respectively to the back and toprof left support channel 5 and bed plate 11 to provide width adjustment and attachment by bolts 15 for adjustable truck mounting angle plate 16. The truck width adjustment assembly is more fully discussed in my co-pending application Serial No. 712,784, filed Feb. 3, 1958, for Chain Driven Electric Tailgate Loader, supra. structure as set forth above is bolted at 17 by means of truck mounting angle plates 13 and 16 to truck side 18 while bed plate 11 rests on truck bed 19 to form an overhanging sill for the structure which protrudes into the back of the truck.

Mounted longitudinally within the U of each support channel 5,, in close spatial relation to back members 5b, are vertical drive screw 20. Each drive screw 20 is rotationally mounted in and held in position by a thrust The U-shapedwelded bearing 21 at the base thereof, which. takes the vertical load of the screw, and by a bronzeor powder bronze type ofoil impregnated bushing 22 atthe. top thereof, which serves to align the screw in a vertical position. Horizontally mounted helical gear 22 mounted on the base of each drive screw above the thrust bearing, partially pro- Sb and is further supported perpendicular to the mounting plane of horizontally mountedhelical gears 22', gain access to helical gears one of the support channels togetherwith electric controls 33 through which the motor is connected to the truck battery and which control the direction of rotation and thus the upward and downward movement of the tailgate lift platform. The unit is designed so that a customer may purchase a manually operated gate and at some later day may buy the completepower mechanism and controls and install them on the tailgate loader,'thus converting it into'a power driven tailgate loader;

Situated on each vertically mounted drive screw 20 is a *block 34 constructed of cast iron or other hard metal containing a hole therein with an internal thread so made as to mate with the thread on the drive screw. Since blocks 34 are situated in the inner space between channels 5 and" 3 and are restrained from turning about screws 20 by frictionless torque balls 47 hearing on back members 5b, as shown clearly in Figs. 4 and 6, as drive screws 20 are rotated blocks 34 must travel either upward or downward in a vertical plane depending upon the direction of rotation of the screws. A pair of frictionless torque balls 47 are mounted along the horizontal center line of thatsurface of each block 34 opposite back member 5b, said balls being symmetrically mounted one on either side of the drive screw in the vicinity of the vertical edges of the block. The torque balls can be mounted in the same manner as anti-friction channel balls 8 and are free to rotate with respect to blocks 34 and roll on back members 5b as blocks 34 travel vertically up and down screws 20 since torque balls 47 are in bearing contact with back members 5b. The pur pose of torque balls 47 is to prevent blocks 34 from jamming channels 5 and 3 due to blocks 34 turning under torsionahmoments transmitted to'themas screws 20 are rotated. Torque balls 47 since they are in hearing contact with back members 5b thus prevent blocks 34 from turning and jamming between channels 5 and 3 as screws 20 are rotated and transmit torsional moments transmitted to blocks 34 as screws 20 are rotated to back members 5b.

The blocks on the two dr-ive screws are aligned so they always remain in a common horizontal plane which travels up and down in the vertical plane. As each block 34rises vertically on its associated drive screws it applies upward pressure to a hardened steel-bearing plate 35 which is bolted at 36 to restraining-plate 37 which in, turn, is welded, to the top of platform lift channel'S, thus carrying the platform lift' channels and the tailgate'lift platform in an upward direction. -.,Steel plates 35 and restraining. plates '37 provide notches shown at 3l8 to allow clearance for drive screws 20. The upward lifting force transferred from-blocks 34 to steel plate 35 of each platform lift channel by means of two magnetized hardened steel lift balls 39: mounted on the top surface of each block, one on each side of each drive screw and mounted on a line throughthe center lines of the two drive screws which is also. parallel With back member 511. Thus by taking the power from the drive screws and transferring it to the movable portion of the tailgate loader by transfer point sources along the drive screw center line, I have freed the vertical drive screws from any torsional bending moment or any other type bending moment caused by a leverage effect the tailgate load would have upon the drive screws. Since there is practically no friction on balls 39 and no way they can transfer any bending moment or torsional bending moment into the drive screws there is no way the drive screws can bind against their associated blocks 34 when a load is put on the tailgate lift platform. This construction also enables the tailgate loader of my invention to be manufactured very simply without fear of mis-alignment causing the lifting mechanism to jam. The hardened steel balls 39 are magnetized to prevent them from becoming dislodged from their seating holes when they are not bearing on steel plate 35 as will be seen later.

On the external face of each platform lift channel 3 in the vicinity of the top end thereof is mounted a lift channel friction ball loading device which consists of a steel friction ball 40 and two mounted steel leaf springs 41 and 42. Friction ball 40 is seated in a hole, designated at 43, in the face of platform lift channel 3. This hole is so designed and positioned as to allow the friction ball to protrude well inside the platform lift channel beyond the closest edge of block 34 and slightly below block 34 when steel plate 35' is hearing on steel balls 39. Friction ball 40 is held firmly in its seat hole 43 by leaf spring 41, which is provided with hole 44 to allow the leaf spring to fit partially over the friction ball and which is welded to lift channel 3. Leaf spring 41 is backed by and. supplied additional spring pressure by leaf spring 42 welded to lift channel 3 through spacer 45. Since there is a friction ball in each lift channel, as blocks 34 are moved downward by rotation of the two vertical drive screws 26* by drive shaft 27, each block 34 will encounter its associated friction ball 40 if the channels, that is channels 5 and 3, of the lowering mechanism stick or hang-up each other. If this should happen, then as each block 34 descends and encounters its associated friction ball it applies a downward pressure on each of the spring-loaded friction balls 40 which in turn transfer this downward force to the platform lift channels 3 resulting in the two channels on both sides of the tailgate being freed. Once freed, the platform lift channels 3 are again lowered by blocks 34 through steel balls 39 bearing on lift channel steel plates 35. When blocks 34 move into contact with friction balls 40, steel balls 39 and steel plate 35 move out of contact and vice versa. When blocks 34 reach the bottom of the drive screws they push the friction balls 40 substantially out of their seating holes 43 and continue downward until they seat against horizontally mounted helical gears 22 mounted on the bottom of the drive screws. Hereinafter in the claims I have referred to the arrangement of the balls 40 in the leaf springs 41 as anti-binding or anti-hang-up means.

The advantage of this lift channel-friction ball loading device is that its construction is extremely simple and trouble-free and that it allows the tailgate loaders to be manufactured much cheaper to a much higher tolerance. The function of the lift channel friction ball loading device is to overcome the adhesive. and cohesive action of the lubricant between the steel support channels 5 and the platform lift channels 3. Due to the large surface areas in contact, the heavy lubricant used and the effects of weather conditions, such as when the units sit outdoors overnight in freezing weather, some device is needed besides the weight of the platform and lift charinels to overcome the lubricant forces between thechannels Sand 3.

With this construction if the platform lift. channels stick in the support channel lift tracks, due to one of the above mentioned reasons, no harm will be done because the lift channel friction ball loading device will catch on the two blocks as they descend on the drive screws and carry the lift channels down with them. Thus by inserting this device on the tailgate loaders, the units can be made much cheaper and still work satisfactorily. Another advantage of this deviceis that/the units can be run almost completely dry of lubrication and still the lift channel-s will slide properly within the support channels because the friction balls will carry the lift channels down as the. blocks move down, and the force of the blocks pushing upward will carry the channels up. The liftchannel friction ball loading device will come into play only during downward movement of the lift channels as implied above. The force transfer system is highly effective because a point surface transfer is maintained by the arrangement of balls as herein described. The advantage of this device over some type of straight spring arrangement is that when the tailgate lift platform is lowered down to the maximum depth allowable by the length of drive screws 20, lift channels 3 and support channels 5, the lift channel friction ball loading device will allow the two blocks to come on past the friction balls by the action of pushing out on the friction balls. This gives an added pro,- tection to prevent mechanism jamming when the tailgate lift platform is lowered down to ground level on sloping ground where the ground beneath the tailgate is lower than the ground beneath the truck wheels, thus causing the tailgate to travel to a lower than normal level. This same action will occur, that is, blocks 34 pushing the friction balls 40 from their seats, if anywhere along the downward travel some serious malfunction freezes the channels within each other. With this action the drive screws, blocks,.helical gears, etc., are protected from jamming and binding, since they can continue operating even though the channels are frozen.

To form the truck tailgate the tailgate lift platform 1 is raised to its extreme'upper limit, truck bed height, as shown in Fig. 1 at 1' and then manually pivoted as indicated by arrows at 46 from the horizontal plane into the vertical plane and locked in place. Of course if there is a load on the tailgate lift platform it must be manually pushed onto the truck bed, after the tailgate has been raised to its upper limit, before the tailgate can be pivoted into the vertical plane. 1

While I have described my invention in certain preferred embodiments, I realize,- however, that modifications may be made and I desire that it be understood that no limitations upon my invention are intended other than may be imposed by the scope of the appended'claims.

What I claim as new and desire to secure by Letters Patent of the United States, is as follows:

1. A vehicle tailgate loader mechanism comprising in combination a pair of drive screws rotatively and vertically mounted within support channel members of U- shaped cross-section rigidly mounted on either side of the tailgate region of a vehicle, said pair of drive screws rotated and connected by a common drive shaft connected to driving means, lift"channel members of smaller U- shaped cross-section contained and longitudinally movable within the U of said support channel members, means for restraining the horizontal movement of said lift channel members, anti-friction means disposed between opposite surfac'es' of said=support channel membersand said lift channel members, lift block members disposed on said drive screws carrying torsion moment transmitting balls thereon disposed along the horizontal center lines of each of the lift block members, bearing plate members securely fastened to the top ends of said lift channel members nor- 7 mal to the longitudinalaxis thereof, anti-torsion and antibending moment coupling means 'disposed between the top surfaces of said lift block members and said bearing plate members, said means being disposed and constituting point surface force transfer means, support channel and lift channel anti-binding and anti-hang-up means mounted on the external face of each lift channel member partly protruding through the face thereof in the vicinity of the lower surface of said lift block member, and a lift platform attached between the lower ends of said lift channel members. a

2. A vehicle tailgate loader mechanism as set forth in claim l'in which said support channel and lift channel anti-binding and anti-hang-up means consists of a springloaded spherical shaped member partially protruding through an aperture, provided in said'lift channel external face, into the interior portion of said lift channel in close spatial relation with and beneath the bottom surface of said lift block member.

3. A vehicle tailgate loader mechanism as set forth in claim 1 in which said support channel and lift channel anti-binding and anti-hang-up means consists of a'springloaded spherical shaped member partially protruding into the interior portion of said lift channel, from the exterior surface thereof so as to intersect the downward travel path of said lift block member.

4. A vehicle tailgate loader mechanism as set forth in claim 1 in which said support channel and lift channel anti-binding and anti-hang-up means consists of a force transferring member spring-loaded in a seating hole on the exterior surface of said lift channel by leaf springs, said force transferring member partially extending through said seating hole beyond and beneath the vertical surface of said lift block member which is opposite the lift channel surface in which said force transferring memher is seated.

5. A vehicle tailgate loader mechanism as set forth in claim 1 in which said support channel and lift channel anti-binding and anti-hang-up means is mounted on the external surface of the rear wall of said U-shaped lift channel member along the longitudinal axis thereof.

6. A vehicle tailgate loader mechanism as set forth in claim l in which said support channel and lift channel anti-binding and anti-hang-up means comprises a spherical shaped member and a leaf spring attached to the ex terior surface of said lift channel member and biased toward said surface, said leaf spring and said lift channel member both having aligned apertures therein of a diam eter substantially less than the diameter of said spherical shaped member for receiving and maintaining said spherical shaped member in position between the apertures in .the surface of said lift channel member and said leaf spring.

7. A vehicle tailgate loader mechanism as set forth in claim 1 in which said support channel and lift channel anti-binding and anti-hang-up means comprises a spherical shaped member and a pair of leaf spring members free at their upper ends and fixed at their lower ends at spaced positions to the external surface of said lift channel member with the free end of one of said leaf springs spring-loading the other of said leaf springs at a position spaced from the fixed end thereof, the spring-loaded leaf spring being apertured adjacent the free end thereof in alignment with an aperture in said lift channel member and a spherical member mounted between and partially contained within the apertures in said spring-loaded leaf spring and said lift channel member and projecting beyond the inner surface of said lift channel member.

8. A vehicle tailgate loader mechanism as set forth in I z p claim 1 in which said means for restraining the horizontal movement of said lift channel members consists of narrow restraining bar members removably secured at spaced positions, corresponding to the depth of the U-shaped cross-section of said lift channel members, to the interior surfaces of the support channel walls forming the arms of the U-shaped cross-section of said support channels.

9.' A vehicle tailgate loader mechanism comprising in combination a stationary U-shaped structure rigidly mounted by mounting means across the rear or tailgate region of a vehicle, a drive screw rotativelymounted within'each vertical arm member of said U-shaped structure, a gear securely attached at the bottom of each of said drive screws mating with corresponding gears disposed on a common drive shaft coupling said drivescrews to a driving means, a longitudinally movable lift channel member of channel-shaped cross-section with one open side thereon disposed within each vertical arm member of said U-shaped structure and about each of said drive screws, a lift block member longitudinally movable along the length of said drive screw disposed on each of said drive screws and carrying on one vertical surface thereof drive screw transmitted lift block torsional moment transmitting means along the horizontal center line of each block member, bearing plate members securely fastened to the top ends of said lift channel members normal to the longitudinal axis thereof, anti-torsion and anti-bending moment coupling means disposed between the topSurface of said lift block members and said bearing plate members, said means being disposed and constituting point surface force transfer means, lift channel anti-binding and anti-hang-up means mounted on the external face of each lift channel member, a portion of which partly protrudes through the face thereof in the vicinity of the lower surface of said lift block member, and a combination tailgate and lift platform member attached between the lower ends of said lift channel members.

10. A vehicle tailgate loader mechanism as set forth in claim 9 in which said lift block members are disposed within the hollow portion of the channel shaped crosssection of said lift channel members in close spatial relation with the interior Walls thereof.

11.' A vehicle tailgate loader mechanism as set forth in claim 9 in which one vertical surface of each of said lift block members is in close spatial relation with the rear wall of one of said vertical arm members of said U- shaped structure while the opposite vertical surface of said lift block member is in close spatial relation with the interior surface of the rear wall of the corresponding lift channel member.

12. A vehicle tailgate loader mechanism as set forth in claim 9 in which each vertical arm member of said stationary U-shaped structure consists of a support channel member of U-shaped cross-section. Y

13, A vehicle tailgate loader mechanism as set forth in torsional moment transmitting means consists of spherical-shaped members rotati-vely mounted on one vertical surface of said lift block member on either side of said drive screw and in bearing contact with the interior surface of the rearwall of said vertical arm member of said U-shaped structure.

i 7 No references cited. 

